Drilling and Bonding to Granite Surface Plate

[jdc3.14]

Searched and didn't find anything about this, if you know of a thread please point me in the right direction.

I'm building a lathe with a long, narrow granite surface plate as the bed. I am going to drill and epoxy inserts to hold linear rails for the ways. Anyone have experience drilling granite? I've seen some people use diamond core drills, and others use carbide tipped masonry type drills. My main concern is tool life, as I need something like 40 3/8" holes and a few 5/8". Also, any recommendations on the epoxy?

I was also wondering if anyone has had experience bonding steel plate directly to granite. I need to mount the z axis screw off the back side and was thinking of bonding drilled and tapped steel as the mount for the bearing blocks. I want to avoid drilling holes here as it will be close to the edge. Then there might be the odd limit switch mount or such that would be nice to epoxy onto the granite.
Any thoughts are appreciated.

 

[jdc3.14]

Edit: Found this thread

Machine screw anchor in granite

I need to place to 2 anchors in the back side of 2cm thick granite. This will alow me to attach this 2"x8" piece to a bracket with 1/4-20 screw. There will be no downward pressure on this but the screws need to be removeable. I checked McMaster and did not find what I had envisioned. There were...

www.practicalmachinist.com

Any other info?

 

[John Garner]

I'm a long, long way from being an expert on the subject, but I've drilled real granite granite and gabbro ("black granite" commonly used for precision stoneware, but not really a granite to the geologists of the world) using carbide-tipped masonry drills.

For adhesive, I've used a whole bunch of different products, from aerospace-grade stuff to hardware-store stuff. I'd suggest a filled epoxy from the hardware store, and have found PC7 works well when a stuff paste is appropriate, as does J B Weld when a flowable consistency is appropriate.

 

[johansen]

A 1$ 10mm diamond core drill might drill 10 holes 1 inch deep. Learned that by experience. Also had to go very slow or they didn't make it that far...

As for the epoxy, it is stronger than the granite. I have a milling machine I built using granite counter top remnants and ordinary Bondo.. that is polyester resin... it really does tear out the granite even after 2 years, bonding to steel that had been freshly ground. Ordinary epoxy is limited to 1500psi bond strength with steel and that requires acid treatment. The epoxy is actually holding on to oxygen atoms bonded to the iron. Aka rust. But you don't want so much rust that you can see it. Iirc you dip the metal in 10% hcl for a few minutes then wash with water then wipe dry.... Then epoxy, and hope to hit 1500psi bond strength.

That being said, a finger print on the granite will prevent the epoxy from soaking in and your bond strength will be near zero. Wet lapping the granite with a diamond stone will restore it. Acetone or other solvents will just spread the oil around.


What you don't want is to find that your 10mm inserts aren't deep enough and the epoxy creeps and the bolts clamping your linear rails loosen up.

Doesn't really matter what the epoxy is filled with. It is best to drill through the granite and bolt through. No epoxy in significant sheer or compression or tension.


I glued strips of mild steel to the granite and then lapped the steel flat (to get rid of the .005" or so global flatness per foot of countertop remnants), then bolted through the granite.


Real granite has substantially higher dampening factor than the synthetic quarts countertop crap. (Which is mostly thermally cured polyester resin and aggravate)

 

[Scottl]

As others have said, a good sharp masonry bit will work, best with a hammer drill. I've drilled old granite surface plates to mount brass plaques.

Clean carefully and use any good epoxy to fasten the inserts.

 

[michiganbuck]

I am also not experienced in doing this but YouTubers show using a diamond coring bit.
I would make a drill location guide bushing perhaps out of a 2x4 or 1" flat board to be clamped to the part, then hang a hot water bottle (large soda bottle) over the hole site, build a dam out of children's modeling clay around the hole site to lead water to my catch bucket, allow my coolant water to gravity to the hole site perhaps through a 1/6 hose ..and begin drilling
Ref:

 

[Pathogen]

Check with Thermatron, some shaker tables are made from granite, and they are drilled and have inserts installed.

Vibration analysis

 

[psionik]

I've done a lot of work as a contractor of various kinds, and drilling into concrete is something I've done many times, and also granite countertops when running plumbing fixtures, etc.

I would use any of those hardware store bought drill bits that has a hex shank on one end and a tube on the other that looks like it's been salted like a margarita glass. Pick one that says "diamond". The carbide ones are used with hammer drills and fracture their way into the material, and I wouldn't risk a precision job with such a bit.

Use a somewhat slow rotation speed (maybe just 600 rpm), and build yourself a little dam out of putty or use a large pan/bucket and tilt the workpiece because you want to keep that bit flooded with water while it drills. (It will last 10 times longer if you do) Pull out to remove any material clogging the hollow inside of the bit now and then but just keep light to medium pressure and be patient. I would do this with a drill press or a magnetic drill just to be sure you're coming down perpendicular to the surface (although granite of course is not magnetic).

As far as epoxy, there are products at the hardware store for bonding rebar into concrete. They come as two large syringes or one double tube that has a nozzle that mixes the 2 parts before it comes out of the dispenser. This stuff will form a very strong bond and will anchor anything quite well so long as you have cleaned out the bore of any dust, water, or grease.

Good luck.

 

[WizardOfBoz]

Can you drill a through hole and use a bolt?

 

[Joe Gwinn]

If I recall, Dan Gelbart made an extreme precision lathe (to diamond turn infrared lenses and the like) with massive granite ways.

 

[Joe Gwinn]

Also, the thermal coefficient of linear expansion of granite and steel differ, so there must be some give somewhere, or the rails will buckle sideways. Look into kinematic constraints and mounts. In the linear case, a ball in circular holes at one end and a ball rolling in a V-groove at the other will do it.